During a concrete pouring process, a material that includes aggregates, cement, and water is poured into an area that may be bounded by forms to contain the concrete material. As concrete is delivered into the pour area, a plurality of laborers, often called “puddlers,” using tools such as rakes, come-alongs, and/or shovels, approximate a uniform distribution of the concrete material to the desired elevation. Still other laborers, commonly equipped with a piece of lumber or other straight member referred to as a “strike-off,” move the strike-off across the concrete material. The process of manually striking-off the concrete material consolidates the material and forces the larger aggregate below the finished elevation. It also shapes the surfaces of the concrete to the desired slope or “grade.” The flatness of the finished surface is highly dependant on the skill of the personnel handling the strike-offs. Additionally, manually striking-off the concrete material is very labor intensive and requires a great deal of skill and experience to ensure a flat and properly inclined finished surface.
The advent of the portable vibratory screed greatly reduced the labor associated with leveling of the concrete material. Portable vibratory screeds commonly include a vibration-inducing mechanism attached to a board or blade and one or more handles that extends from the blade. The vibration mechanism typically comprises an “exciter” formed from one or more eccentric weights driven by a motor. Operation of the vibration mechanism consolidates the concrete material such that, as the blade is moved across the wet concrete, the vibrating blade forces the larger aggregate below the surface of the material and works a highly cementatious material with smaller aggregates, often called “cream,” to the finish surface of the material. Operator manipulation of the handle, as well as the rigidity of the blade, directly affects the flatness and inclination of the finished surface of the material. Accordingly, an operator's ability to control the pitch or tilt of the blade as well as the speed and direction of travel of the blade determines the flatness of the finished material.
To reduce the transmission of vibrations to the operator's hands from the vibration mechanism, an isolation mechanism, such as a rubber bushing, is commonly disposed between the end of the handle and the blade. However, the isolation mechanism provides an undesirable response to handle movement during operation because the isolation mechanism distorts upon handle movement so that only a portion of the effect of the handle's motion is translated to the blade. Accordingly, the isolation mechanism detrimentally affects the operator's ability to control the position of the blade.
The elevation of the finished material is also commonly determined by the operator's visual inspection of the finish elevation in relation to the elevation references such as the forms. Although portable vibratory screed assemblies are known which include various inclination indication systems, such systems are commonly directed to targeted users. Many inclination and elevation systems include laser systems. However, many such systems fail to address the positioning of the handle, and thereby the pitch of the blade, relative to the bottom surface of the blade. As such, such laser elevation systems are only somewhat successful at properly indicating to the operator the direction the handle should be moved to acquire an elevation and/or pitch that is consistent with the desired elevation. Additionally, the laser elevation and inclination systems are costly to integrate into a screed. From a manufacturing perspective, these costs are commonly deferred to the customer as well as the costs associated with the service and maintenance requirements of such systems.
Others, such as the system disclosed in U.S. Pat. No. 4,752,156, have relatively inexpensive inclinators, such as a site level, for indicating the orientation of the screed plate. A site level, often known as a bubble vial, is formed from a glass tube having a bubble encased in a liquid. The bubble is centered in the vial when the vial is horizontal and rises toward one end or the other if the vial is inclined relative to the movement. However, as discussed in U.S. Pat. No. 6,758,631 the '631 patent, such indicators have been less than successful at indicating the inclination of the blade of the screed during operation of an exciter assembly. That is, vibrations generated by operation of the exciter assembly propagate to the bubble vial and obliterate the bubble of the site level, rendering it useless. The '631 patent concludes that bubble vials or site levels are unacceptable for screed inclination indication during screeding.